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    <title>ShellCheck: SC2234 – Remove superfluous `(..)` around test command to avoid subshell overhead.</title>
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    <h1>SC2234 – ShellCheck Wiki</h1>
    <a href="https://github.com/koalaman/shellcheck/wiki/SC2234">See this page on GitHub</a>
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    <h2
id="remove-superfluous--around-test-command-to-avoid-subshell-overhead">Remove
superfluous <code>(..)</code> around test command to avoid subshell
overhead.</h2>
<h3 id="problematic-code">Problematic code:</h3>
<div class="sourceCode" id="cb1"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb1-1"><a href="SC2234.html#cb1-1" aria-hidden="true" tabindex="-1"></a><span class="kw">(</span><span class="bu">[</span> <span class="st">&quot;</span><span class="va">$x</span><span class="st">&quot;</span> <span class="ot">-gt</span> 0 <span class="bu">]</span><span class="kw">)</span> <span class="kw">&amp;&amp;</span> <span class="ex">foo</span></span></code></pre></div>
<h3 id="correct-code">Correct code:</h3>
<div class="sourceCode" id="cb2"><pre class="sourceCode sh"><code class="sourceCode bash"><span id="cb2-1"><a href="SC2234.html#cb2-1" aria-hidden="true" tabindex="-1"></a><span class="bu">[</span> <span class="st">&quot;</span><span class="va">$x</span><span class="st">&quot;</span> <span class="ot">-gt</span> 0 <span class="bu">]</span> <span class="kw">&amp;&amp;</span> <span class="ex">foo</span></span></code></pre></div>
<h3 id="rationale">Rationale:</h3>
<p>You are wrapping a single test command in <code>(..)</code>, creating
an unnecessary subshell. This serves no purpose, but is significantly
slower:</p>
<pre><code>$ i=0; time while ( [ &quot;$i&quot; -lt 10000 ] ); do i=$((i+1)); done
real    0m6.998s
user    0m3.453s
sys     0m3.464s

$ i=0; time while [ &quot;$i&quot; -lt 10000 ]; do i=$((i+1)); done
real    0m0.055s
user    0m0.054s
sys     0m0.001s</code></pre>
<p>Just delete the surrounding <code>(..)</code> since they serve no
purpose and only slows the script down.</p>
<h3 id="exceptions">Exceptions:</h3>
<p>This issue only affects performance, not correctness, and can be <a
href="ignore.html">ignore</a>d for stylistic reasons.</p>
<h3 id="related-resources">Related resources:</h3>
<ul>
<li>Help by adding links to BashFAQ, StackOverflow, man pages, POSIX,
etc!</li>
</ul>
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    <p style='font-size: 80%'><a href="../index.html">ShellCheck</a> is a static analysis tool for shell scripts. This page is part of its documentation.</p>
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